Teen Gothic

I’m sure I’m not the first person to ask this, and I probably won’t be the last, but I find post-punk “purists” very confusing and want to see what you guys think. Essentially I’ve heard people argue that modern goth music “isn’t goth” and is rather something else entirely, but why? I never see anyone call modern rock bands anything but rock (ignoring sub-genres), but none of them sound like the Stones or, hell, the Beatles. Why do some people hold our music to the same standard when the point is for it to keep evolving? I mean wouldn’t the same thing over and over again get stale and boring after a while?